Heteroaromatic ring modified naphthalimide interlayer materials for efficient polymer solar cells

Abstract

We design and synthesize four naphthalimide (NI)-based organic cathode interlayer materials (CIMs) end-capped with electron-withdrawing heteroaromatic rings, namely NTDC, NTR, NTRIC and NTTC. Compared with NTN (bis(N-dimethylaminopropyl)-4-thiophene-1,8-naphthalimide), a reported CIM, these four CIMs show red-shifted absorption spectra, slightly elevated energy levels, enhanced π-π stacking, and increased surface wettability and roughness. Specifically, NTR terminated with rhodanine unit exhibits increased electron mobility and conductivity, uniformly distributed rodlike surface morphology, superior thermal stability, and stabilized NTR/electron acceptor contact. Moreover, binary PSCs based on NTR interlayer obtain a power conversion efficiency of up to 18.9%, which is the highest among reported NI CIM-based binary devices, and present enhanced device thermal stabilities. This study provides an effective approach to design efficient and thermally stable NI-based CIMs through heteroaromatic terminal-group strategy for application in high-efficiency nonfullerene PSCs.